1. Field of the Invention
This invention relates in general to electronic circuits for varying a voltage output, and in particular to a circuit for firing silicon controlled rectifiers.
2. Description of the Prior Art
Silicon controlled rectifiers, hereinafter referred to as SCRs, can be used for providing variable power output. An SCR has a cathode and an anode, one of which may be connected to an AC power supply. The SCR has a gate which when fired, will allow the AC current to pass through the SCR. The SCR will conduct until the voltage reverses polarity. In general, the amount of power output through the SCR depends upon when the gate is fired. If fired early in the AC cycle, more power will flow through the SCR than if fired late in the cycle.
Phase locked loop circuits have been used to insure the operation of a local oscillator at the same frequency as a "reference" signal. A phase locked loop can also detect the amount of change from that frequency. These circuits, however, are expensive and complex.